1. Field of the Invention
The present invention relates to a manhole cover assembly for mounting a manhole cover above a manhole basin. The invention is applicable to adjustment of the slope of the manhole cover, and usually also its height, as necessitated by resurfacing a road surface and/or by frost heave of the surrounding ground.
2. Prior Art
Manhole basins, which may be a sewer basin having an inlet and an outlet, or may be a catchment basin having only an inlet, are normally cast of concrete. A frame of metal is fixed to the top of the concrete basin and holds the manhole cover. In order to keep the cover level with a road or ground surface it is frequently necessary to alter the height between the manhole cover and the top of the basin, particularly in regions where there is much frost heave; adjustment to the height is usually done when a road is resurfaced. Adjustment of slope may also be necessary, as when the camber of a road is changed. In addition, adjustment of the lateral position may be necessary, especially with catchment basins where the manhole must be positioned accurately close to a curb.
Various constructions of adjustable manhole frames have been proposed to deal with height adjustment and to avoid replacing concrete parts. In some cases, screw jacks have been used between the annular frame which holds the cover and the top of the concrete manhole basin. In others, an outer ring, supported by the basin, has internal helical threads of large diameter within which is an inner ring having mating screw threads, and which is rotatable to adjust its height. Examples of patents showing such systems are:
U.S. Pat. No. 3,533,199, which issued Oct. 13, 1970 to Pickett;
U.S. Pat. No. 3,629,981, which issued Dec. 28, 1971 to McCaffrey;
U.S. Pat. No. 4,075,796, which issued Feb. 28, 1978 to Cuozzo;
U.S. Pat. No. 5,095,667, which issued Mar. 17, 1992 to Ryan et al.; and
U.S. Pat. No. 5,344,253, which issued Sept. 6, 1994 to Sacchetti.
All the above patents are concerned with height adjustment, and show little or no provision for slope adjustment. Most of the patents show upper and lower parts of the frame assembly to be connected by helical threads surrounding the annular upper portion of the frame so that rotation of this upper portion changes its height without any change to its slope. However, some other patents show jack-type screw adjusters which are spaced around the frame and which can be adjusted individually to alter the slope, as well as the height, of the upper frame portion. Such arrangements are shown in the following patents.
U.S. Pat. No. 3,930,739, which issued Jan. 6, 1976 to Larsson et al,;
U.S. Pat. No. 4,149,816, which issued Apr. 17, 1979 to Piso; and
U.S. Pat. No. 4,925,337, which issued May 15, 1990 to Spiess et al.
These prior arrangements would appear to have some drawbacks. In particular, they seem to offer only limited slope adjustment. This is especially true of Piso, where more than slight change of slope would seemingly cause binding in the adjusting screws. In Larsson et al. and Spiess et al., the amount of slope adjustment would be limited by binding between outer edges of the upper frame portion and the fixed surrounding structure. Also, these prior patents do not show any seals which would prevent ingress of soil or other material into the mechanical parts if there were to be significant slope adjustment. Larsson et al, and Piso show small seals which would accommodate only a small amount of slope adjustment, while Spiess et al. show no seal at all.
It is an object of this invention to provide an adjustable manhole assembly in which substantial slope adjustment of the manhole cover is possible.
A further object of embodiments of the invention is to provide a joint arrangement which can maintain a seal against soil and other material entering the manhole basin even when substantial adjustments are made.
The present invention overcomes the deficiencies of the prior art in relation to slope adjustment by providing at least one part-spherical mating surface between an upper part of the assembly which is subject to slope adjustment and a lower part which remains stationary.
Preferably, the slope adjustment does not separate the mating surfaces.
In a preferred embodiment, the invention allows lateral adjustment of the cover position such as will allow the cover to be set a precise distance from the curb.
In accordance with one aspect of the invention, an adjustable manhole basin cover assembly including an upper section of an annular manhole basin comprises:
an upper annular part having a recess for receiving a manhole cover and adapted to mate with an underlying annular surface which is also part of the assembly, the upper annular part and the underlying annular surface having mating surfaces,
wherein at least one of the mating surfaces is part spherical, whereby the upper annular part may be adjusted in slope relative to the upper manhole basin section while maintaining a sealing relationship between the mating surfaces.
Preferably, both of the mating surfaces are part spherical. Also, the mating surfaces are preferably surrounded by a sealing collar to minimize entry of soil or other matter between these surfaces.
The upper annular part may be an adjustable frame assembly for variably spacing the manhole cover above a conventional concrete manhole upper section, in which case the concrete manhole basin upper section and the bottom of the frame assembly have the part spherical mating surfaces.
Alternatively, the upper annular part may be an upper portion of the adjustable frame assembly, and the part spherical mating surfaces are provided between the upper portion and a lower portion of the frame assembly.
Preferably, spherical mating surfaces are used both between the manhole basin upper section and the frame assembly, and between upper and lower portions of the frame assembly. The lower mating surfaces between the manhole basin upper section and the frame assembly provide a coarse adjustment, while the upper mating surfaces between the upper and lower portions of the frame assembly provide a fine adjustment. The provision of two slope adjustments, by the upper and lower pairs of mating surfaces, also has the advantage that the adjustments can be combined to give some lateral adjustment of the upper portion of the frame assembly.
A greater degree of lateral adjustment may be provided by a modified construction in which the precast manhole basin upper section, which has one of the part spherical mating surfaces, is in the form of a precast adapter ring resting on a manhole basin upper section with an annular upper surface, which may be the conventional flat top of a manhole upper section. In this case the manhole cover assembly of this invention can be considered as including this adapter ring as well as the frame assembly resting on it. For the lateral adjustment, the precast adapter ring has its annular top surface formed eccentrically to its lower surface so that the lateral position of the frame assembly relative to the manhole basin can be changed by rotating the precast adapter ring on the manhole basin.
According to a second aspect of the invention, an adjustable manhole cover assembly comprises:
a precast manhole basin upper section having an annular top surface, the upper section being in the form of a precast adapter ring having an annular top surface and annular lower surface, the annular lower surface being suitable for resting on a manhole basin with an annular upper surface; and
a frame assembly having a recess for receiving a manhole cover, the frame assembly having an annular lower surface capable of resting on the annular top surface of the adapter ring so that the last-mentioned annular surfaces form mating surfaces, at least one of said mating surfaces being part-spherical so as to allow slope adjustment of the frame assembly relative to the adapter ring;
the precast adapter ring having annular top surface formed eccentrically to its lower surface so that the lateral position of the frame assembly relative to the manhole basin can be changed by rotating the precast adapter ring on the manhole basin.
Where the manhole cover assembly has an adjustable frame assembly with a recess for receiving a manhole cover, and has an annular lower surface capable of resting on an annular top surface of a precast manhole basin upper section, the adjustable frame assembly may have an inner frame movable within an outer frame for adjusting the height of the inner frame, and part spherical mating surfaces may be provided on upper and lower portions of the inner frame. As in prior art constructions, the inner frame may have external helical threads engaging internal screw threads of the outer frame, whereby these threads may be used to adjust the height of the inner frame relative to the outer frame for raising the height of the manhole cover support.
The invention may also provide a special locking arrangement for locking the manhole cover in place on the frame assembly.